¼ cup granulated sugar (optional, for extra sweetness)
Instructions
Preheat oven to 350°F. Grease or line an 8×8″ baking pan with parchment paper.
In a medium bowl, whisk together flour, baking powder, and salt.
In a large bowl, beat softened butter with granulated and brown sugars until creamy. Add egg and vanilla, mixing well. Gradually add dry ingredients, mixing until just combined. Press dough evenly into the bottom of the pan.
In a medium bowl, whisk lemon juice, granulated sugar, flour, and salt until smooth. Add eggs one at a time, mixing well after each. Stir in melted butter. Pour lemonade filling over the cookie base.
In a small bowl, combine crumble topping ingredients and mix with a pastry cutter or fingers until coarse crumbs form. Sprinkle evenly over filling.
Bake for 30–35 minutes, until filling is set and topping is golden brown.
Cool completely before cutting into squares. Optionally, sprinkle with extra sugar.